1. Field of the Invention
The present invention relates to repair of a defect in the vascular wall for vascular surgery and to repair of a defect in the dural membrane for spinal and cranial surgery. More particularly the present invention relates to a surgical method and surgical clamping system for vascular repair and/or for dural membrane repair using opposed clamping plates having coiled ribs.
2. Background Information
Dural Membrane
The dura 10 (see FIG. 1), also called dural membrane and dura layer, is a layer of the membranous sac which covers the two parts of the central nervous system, the brain and spinal cord. A layer of fluid 12, termed cerebrospinal fluid, is present in the sub-arachnoid space between the dura and the structures of the central nervous system (i.e. the brain 14 or the spinal cord) and functions as a cushion as shown in FIG. 1. The other layers, the arachnoid layer 16 and pia layer 18, are very thin and structurally not significant for the purposes of the discussion in this application. The arachnoid layer 16 and the pia layer 18 are typically not specifically addressed in the repair of a rip, cut, rupture, tear, piercing or other defect in the dural membrane 10, in which a defect will generally also affect these structures. The term defect is used generically herein to reference all discontinuities in the membrane surface, including cuts, tears, naturally forming defects, rips, ruptures, piercing, or other break in the membrane surface.
The dura 10 is often damaged during surgery and requires repair so that cerebrospinal fluid 12 remains contained. A cerebrospinal fluid leak places the patient at substantial risk for meningitis (infection surrounding the brain), and generally causes a severe headache since the brain 14 sags without the supportive function of the fluid 12. The dura 10 is damaged purposefully (e.g. cut), on occasion, so that surgeons can access the underlying spinal cord or brain 14. Other times, the dura 10 is inadvertently injured during the course of spine surgery where access to the spinal cord is not required, i.e. removal of a herniated disc. The rate of inadvertent spinal fluid leaks due to dural membrane damage occurs in about 5% of open spinal procedures.
The numerous dural membrane repair methods can be generally categorized into: (a) those that re-approximate the edges of the defect (i.e. sutures or staples), (b) those that seal the defect with some type of glue, and (c) lastly, those that place a patch over the defect. Oftentimes, a combination of these strategies is used; however, significant drawbacks, which will be detailed further, are associated with each of these methods.
The first category of techniques, re-approximation of the edges, is the current method of choice and is represented in FIGS. 2a and 2b. Most commonly, fine suture 20, such as 4-0 silk available from US Surgical or 5-0 prolene available from Ethicon, is used to repair the dural defect. The suturing method is highly effective, but it is often not an option because of problems with either visualizing the dural membrane defect or with having enough room in the incision to manipulate the needle driver at the proper angle. Visualization of the defect 25 in the dura 10 can be difficult because the spine is often approached from the posterior (back) during surgery, as represented in FIG. 3, but the defect may occur in the anterior aspect (front) of the thecal sac. The spine 22, in FIG. 3, is being viewed behind and slightly off to the left of the patient. One analogy used to explain this relationship of elements is that the spine 22 is like a tunnel and the dural tube 10 is like a long worm going through it. The roof of the spinal canal is dissected away in FIG. 3 exposing the back and left side of the dural tube 10. Typical surgical exposure is rarely as good as shown in FIG. 3. The front and the sides of the dural tube 10 are essentially inaccessible to suturing instruments when the approach is from the posterior (back). Moreover, the back (side facing the surgeon) of the dural tube 10 is also extremely difficult to suture especially when the exposure is limited, as in microsurgery spine cases particularly when minimally invasive techniques such as endoscopes or tubes are used.
In an effort to provide surgeons with a tool that could compensate for the shortcomings of the suturing technique, titanium dural staplers, such as US Surgical's Auto Suture VCS™ disposable clip applier, were developed. These staplers possess the advantage of being able to work in tighter spaces; however, effective application is technically difficult for a number of reasons. One such reason is that these staplers are bulky and impede visualization of the affected area. Another frustrating problem is that the staples are difficult to place accurately, and to make matters worse, the staples have a known tendency to slip off.
The second major strategy for the repair of dural defects is the use of glues which are also referred to as tissue sealants. These glues are gelatinous masses that cover the defect, but do not actually glue the edges of the dura 10 together. Most of the approved biological sealants work through the basis of creating a fibrin mesh. When used by themselves, glues such as Tisseal™, are associated with significant drawbacks. One potential shortcoming is that tissue sealants require dry conditions to set; however, the spinal fluid leak is by definition a wet condition thus precluding use. Another concern is that the adhesive and tensile strength of the formed gels are lacking. Fluids tend to leak around the gelatinous mass, which is not firmly attached to the dura, or dissect through it. Because of these limitations, tissue sealants are commonly used as a supplement to other dural membrane closure techniques.
The third major tactic for repairing cerebrospinal fluids leaks is the use of a graft to patch over the defect. Several types of patches are available ranging from those harvested from the patient to those of the synthetic variety. The handling characteristics of these grafts vary widely and as such each type will be individually discussed.
Harvested grafts include those consisting of fat and muscle. If possible these patches are placed into the defect as a plug; otherwise, they are used like a blanket to cover the dural membrane defect, such as represented in FIG. 4. Sometimes the fat or muscle is secured to the dura 10 with stitches. Overall, these natural patches are effective and are used especially in cases where the spinal fluid leak is difficult to stop. The main drawbacks, however, are that significant additional tissue trauma is incurred with the act of harvesting, and that achieving a secure “plug” is not easy.
One alternative to fat and muscle grafts is bovine pericardium such sold under the brand name Duraguard™ by Synovis. In using animal tissues, the patient is spared the additional trauma of harvesting. However, since pericardium possesses no inherent stickiness to dura 10, it is a patch that must be sutured in water tight fashion into the defect. While it is often used to repair extremely large dural membrane defects for brain surgery, the need to suture the perimeter of the Duraguard™ patch to the free edges of dura 10 essentially precludes the use of this technique in the spine. Patches made of synthetic collagen matrices represent an additional option that is commonly employed. The difference between these patches, such as sold under the brand Duragen™ sold by Integra, and the bovine pericardium patches is that they possess some inherent stickiness to the dura 10 that allows the Duragen™ patches to be placed over the defect and secured without the use of sutures. This feature allows for more ready utility in the spine procedures. However, without sutures, the seal is tentative, and is usually reinforced with a tissue sealant. Even this combination of the patch and tissue sealant is far from secure. As with the previously described methods, patients often have an extended hospital stay, remaining flat in bed for 3 to 5 days, to allow for healing so that the dura 10 is sealed. This form of graft is particularly effective for fixing dural membrane leaks that are difficult to visualize. A competing patch type dural membrane repair product is manufactured by Codman.
By using a combination of current dural membrane repair techniques, most dural membrane defects can be fixed. The drawbacks either relate to technical difficulty, additional patient suffering and cost, or lack of certainty. It will be difficult to improve the dural repair methods that exist currently through improvements in the specifics of these techniques alone. Advancements in suture and staple technology will have to overcome the fact that a suture/staple line will always be more prone to leaks than a solid seal, and will also be more time consuming. Though a large amount of sealant technology research is being performed, there is considerable difficulty in finding glues that will attach to wet surfaces and remain biocompatible at the same time. Graft technology, such as Duragen™ brand grafts, will also require a substantial leap to overcome the lack of adherence to dural membrane edges. However, they will continue to serve a function particularly when the dural membrane defect cannot be easily visualized.
As spine surgery progresses more and more from traditional large open incisions to minimally invasive surgery, the limitations of current dural membrane closure techniques have become more apparent since the mainstay, the traditional suturing techniques, become even more difficult to perform If a new device could safely, effectively and rapidly close dural tears, then the current techniques could be readily supplanted as well as adding to the armentarium of tools for true minimally invasive procedures. In our opinion, there is a growing need for effective and efficient surgical methods and apparatus for the repair of defects in the dural membrane.
Blood Vessels Trauma
Similar to the dural tube, blood vessels also possess a lumen. Blood vessels in the body are of two types, arteries that carry blood from the heart to other organs and veins that carry blood from the body back to the heart and lungs so that re-oxygenation can occur. Blood in arteries is under high pressure, and as a result, arteries have a relatively thick wall which can be comparable to that of the dura. The diameter of arteries varies considerably from millimeters to about 3 centimeters (the aorta). The pressure in veins is low, and as a result, the walls are very thin.
Blood vessels are often injured from trauma or inadvertently during surgery. Repair of blood vessels is performed in the fields of trauma surgery, transplant surgery, neurosurgery, cardio-thoracic surgery, vascular surgery, orthopedic surgery, and general surgery. Failure to repair damaged blood vessels can lead to death by exsanguination, stroke, venous insufficiency, and loss of an organ or limb.
When blood vessels are damaged, surgeons most often will elect to sacrifice the vessel using methods such as suture ligation, vascular clips, and electrocauterization. Removing the artery or vein from circulation is extremely effective in addressing blood loss, but a poor option if the damaged blood vessel has an important function. For example, obviously grave consequences would occur if the aorta, the main artery of the body, was ligated.
Several techniques can be used to repair damaged blood vessels while preserving them at the same time. One common method is the application of a thrombin soaked sponge or a hemostatic gel to the bleeding vessel. These devices cause a clot to form and are very effective at stopping low pressure and low flow bleeding. The limitation of this method is that vigorous bleeding cannot be easily controlled. Numerous companies (Tisseal, Surgifoam, Surgicel, Avitene, Fibrillar, Flowseal) make commercial versions of this device.
Another hemostasis technique is the use of suture to close the defect in the blood vessel. The success of this method varies according to the surgical exposure, size and type of blood vessel. Large arteries and veins can be sutured under optimal conditions. However, placing these sutures is time consuming and often causes critical narrowing the vessels which could lead to inadequate circulation.
A third option is the use of electro-cautery techniques to close the defect. In this method a device such as the bipolar or electrosurgical pencil causes the tissue surrounding the defect to shrink and hopefully close the gap. Only very small defects with low flow bleeding can be treated with this technique and the risk of damaging the normal portions of the affected blood vessel is substantial.
One final alternative to closure of defects in blood vessels is the use of a patch. These patches can be natural (i.e. saphenous vein graft) or synthetic (Dacron® or polytetrafluroethylene (PTFE-Goretex®). Furthermore, they exist in different configurations such as a flat patch or in the form of a tube. Their use as a device to close vessel wall defects is limited for several reasons. First and foremost is the technical difficulty of sewing in these grafts particularly when time is of the essence and exposure is less than optimal as occurs in a emergency situations. Second, placement of these grafts necessitates a large surgical exposure which may not exist. Lastly, many of these grafts do not exhibit long term patency.
Taken together, the current the above described commercial methods for repair of damaged blood vessels possess limitations similar to those associated with existing methods of dural membrane repair. There is a need for effective and efficient surgical methods and apparatus for the repair of defects in vascular walls.
Blood Vessel Surgical Puncture
It a related but slightly different vascular repair field is the repair of the intentional damage or defect in a blood vessel. Numerous medical procedures are performed which require formation of a puncture or the like in a blood vessel for the introduction of various devices, such as catheters. Access to arterial and venous vascular systems is necessary for both diagnostic and therapeutic medical procedures. For example, diagnostic arteriography is a radiologic procedure which permits visualization of the arterial system for the diagnosis of disease in various organ systems. Some frequent applications are cardiac catheterization, peripheral vascular angiography, mesenteric angiography, and cerebral angiography. Therapeutic trans-arterial procedures, such as percutaneous transluminal coronary angioplasty, have expanded the use of arterial access even further. All these representative techniques involve cannulation of an artery so that a catheter may be inserted and advanced into the arterial system.
The femoral artery at the junction of the thigh and the abdomen is the most frequent arterial puncture site, but the carotid artery in the neck, the brachial artery in the mid-arm, and the axillary artery are also used. A percutaneous sheath is usually used whenever multiple catheters are used. When the sheath is removed, the remaining 1.5 to 5.0 millimeter hole in the artery would spurt blood with significant blood loss unless certain measures are taken. Effective arterial puncture sealant devices have been proposed, such as described in U.S. Pat. Nos. 4,744,364; 4,852,568 and 4,890,612, for the mechanical sealing of-such punctures. In such cases, a sealing device in the form of an expandable closure member is to be inserted through a puncture in the vessel, expanded while within the vessel and then retracted against and through the puncture by means of a retraction filament. Thereafter, the filament is left extending from the site of the puncture and through the skin of the patient while being secured in position on the skin of the patient as by a strip of conventional tape. However, such devices permit the exposed thread to be a site for infection. Further, anchorage of the enclosed member in place by a thread which passes through the skin of a patient may not be reliable so that bleeding may occur by accidental displacement of the sealant device. Further, displacement of the sealant device into the artery would result in arterial occlusion and gangrene.
U.S. Pat. No. 5,350,399 proffered a somewhat better solution for sealing a puncture wound in the form of sealing device is composed of an intra-arterial occluder and an extra-arterial occluder, both made of resilient biocompatible and/or bioabsorbable material and held in place via a saw-toothed guide extending integrally from the intra-arterial occluder. However the clamping configuration proposed in this patent is not optimal for other vessel defects outside of the well defines small puncture wound. Improvements can be made to the inner occluder and outer occluder and the guide there between to make this type of clamping vessel repair solution more effective and more practical to a wider variety of vessel repair applications.